Question

A buffer is prepared by combining a weak acid or base with its conjugate form. A buffer is made using 0.1 M KH2PO4 and 0.1 M K2HPO4. Which component of the buffer is the acid and A)which is the conjugate base? B)write the equation for the reaction between the buffer and the strong acid,HCL? C)write the equation for the reaction between the buffer and the strong base,NaOH? d)if the pKa of the weak acid is 7.21, using the Henderson Hasselbach equation, what will be the ph of the buffer if equal volumes of two buffers components are mixed? e) what would the effective pH of the buffering range be for this buffer?

Answer 1

A)which is the conjugate base?

KH2PO4 will give H2PO4- and K2HPO4 will give HPO42-

H2PO₄^-(aq) + H2O(l) ------> HPO₄^2- (aq) + H3O⁺  , pKa = 7.21

Acid     base          conjugate base conjugate acid

A pair of molecules or ions related to each other by loss or gain of a single is called a conjugate acid-base pair

Here the conjugate base HPO₄^2- (aq) or K2HPO4

B)write the equation for the reaction between the buffer and the strong acid,HCL?

HPO₄^2- (aq) + HCl (aq) ----> H2PO₄^-(aq) + Cl-

C)write the equation for the reaction between the buffer and the strong base,NaOH?

H2PO₄^-(aq) + NaOH (aq) ---- > HPO₄^2- (aq) + H2O

d)if the pKa of the weak acid is 7.21, using the Henderson Hasselbach equation, what will be the ph of the buffer if equal volumes of two buffers components are mixed?

Hendersen equation

pH = pKa + log [HPO₄^2-(aq)] / [H2PO₄^-(aq)]

pH = 7.21+ log 1.0

pH = 7.21+ 0.0

= 7.21